Crucible

A container in which glass is melted so that it can poured.

A crucible can be free standing, so that it is lifted with tongs and poured. It can also be part of a plaster (or other) mold. When it is part of the mold, the crucible is charged (filled) at room temperature so that as the kiln heats the glass runs into the mold's design elements below the crucible.